1. Field of the Invention
The present invention relates to a multi-pole molded case circuit breaker, more particularly, to a multi-pole molded case circuit breaker having a safety device (with an isolation function) which prevents a manipulation handle from being moved to an off-position when a fusion occurs on a contact part.
2. Description of the Conventional Art
In general, an MCCB (Molded Case Circuit Breaker) is a device which protects a circuit or load by cutting-off a circuit when an abnormal current or an overload is generated. Further, a multi-pole molded case circuit breaker is a kind of a molded case circuit breaker having a plural-phase, such as a 3-phase circuit. For instance, when the 3-phase circuit includes a neutral polarity, the circuit breaker may be a 4-pole circuit breaker including a 4-pole (R, S, T and N poles).
FIG. 1 is a view illustrating a longitudinal section of a base module of a multi-pole molded case circuit breaker.
In FIG. 1, there is not shown a case, but an open/close device coupled to a base mold 15 and a part related to a contact part.
FIG. 2 is a perspective view illustrating the base module of FIG. 1. In FIG. 2, the base mold 15 is not shown and parts are shown separately by each phase.
FIG. 3 is a disassembled view illustrating a partial open/close device including a handle of FIG. 2.
In a general multi-pole molded case circuit breaker, a shaft is manufactured in the form of module with a base mold by each phase, such as R, S, T and N in order to reduce production cost and increase manufacturing efficiency. That is, fixed contacts, movable contacts, a shaft assembly, an arc chamber, and the like are molded in the type of block within the base mold of each phase, and such a blocked parts are disposed within a separate outer case, then the multi-pole molded case circuit breaker is manufactured. By manufacturing each pole (phase) of the multi-pole molded case circuit breaker in a modularized part, it is possible to reduce production cost and increase assembly performance and productivity.
According to such a modularized multi-pole molded case circuit breaker, there is advantage in the sense of manufacturing, while involving disadvantage in that since durability (resistance) against a bending load is low, compared to a single-type molded shaft, a load may not be uniformly transferred to each phase in the mechanism.
First, the structure and operation of a module type multi-pole molded case circuit breaker will be described as follows.
An open/close device includes a toggle link (not shown) and a release device 9 which are coupled to a pair of side plates 11. The toggle link device includes an open/close lever 2 which is rotatably connected to a handle 1, and an upper link 3 and a lower link 4 which are connected via a link shaft 5, and disposed between a movable contact 6 and a latch 7.
A release device 9 is connected to the latch 7 and a latch holder 8 and is configured to release the latch 7 by interworking with an operation of an over-current release device (not shown). A main spring 10 is disposed between the open/close lever 2 and the link shaft 5 of the toggle link device.
The switching operation of the multi-pole molded case circuit breaker is carried out as follows.
When a handle 5 is rotated to an OFF-position from an ON-position, an upper link 3 and a lower link 4 of the toggle link device are bent in “>”-shape with an elastic force of the main spring 10 so that the movable contact 6 is separated from the fixed contact 14, thereby causing the circuit to be opened.
Further, when an over-current release device (not shown) is operated due to an overcurrent which flows through the circuit, the release device 9 is operated by the output of the over-current release device to release a latch 7 which is caught by the latch holder 8. As a result, the latch 7 is rotated in counterclockwise direction and the open/close device is tripped so that the movable contact 6 is opened to cut-off a current. And the handle 1 is moved to an intermediate position between the ON and OFF positions together with the open/close lever 2 to indicate a trip operation. Further, when the circuit breaker is reclosed after the trip operation, the handle 1 is moved to an ON-position after moving to an OFF-position to reset a release device 16, the movable contact 6 is closed.
In the multi-pole molded case circuit breaker, when a fixed contact 14a and a movable contact 6a are fused due to an overcurrent which flows in the main circuit in a conductive (ON) state, the movable contact 6 is not moved so that contacts of the main circuit are in contact with each other though an overcurrent release device (not shown) is normally operated, and in such a condition the handle 1 is stopped at an ON-position.
However, it is possible to move the main spring 10 to an OFF-position by applying a larger force to the handle 1 than as usual even in a state that the contacts of the main circuit are fused and integrated, so that the circuit breaker is stopped. In this instance, a user may misunderstand the circuit breaker to be opened so that he may execute an investigation or maintenance work, thereby causing a safety accident such as an electric shock.
To prevent such a safety accident, the circuit breaker may have a function (an isolation function) to prevent the handle from being rotated to an OFF position even in a case that contacts are fused in a conductive condition. Such an example may be referred to as Korean Patent No. 10-0697507 (equivalent to JP Patent No. 3972782 and U.S. Pat. No. 6,924,720).
However, the conventional modular type multi-pole molded case circuit breaker does not provide an isolation function, considering a displacement phenomenon by an inclination (bending) between each phase. In such a conventional modular type multi-pole molded case circuit breaker, there is provided a shaft pin which connects each shaft in order to convey a rotational force of an open/close device to each phase.
Referring to FIG. 4, in the modular type multi-pole molded case circuit breaker, since the shaft 12 of each phase is divided, the shaft pin 13 is inclined so that an inclination may be generated. Thus, shaft 12 may rotate more than a design value, so that the main spring 10 exceeds a dead point and the handle 1 passes away an OFF-position, thereby occurring faulty. For instance, when the R-phase is fused, a height of the shaft pin 13 of the T-phase may differ by a predetermined gap. As a result, there is a disadvantage in that the shaft 12 may be rotated at a predetermined gap so that it may be misunderstood that it is a normal state even in a fused state.